High Idle Temperature

[down_shift13]

Hi, I have a 1989 325i coupe. Recently, I noticed that my temperature climbs a little past the 1/2 mark. I thought this was the Fan Clutch, so I replaced that. Also I found out that my Aux fan was not turning on so, I replaced the thermo-switch and the resistor. I got the Aux fan to work with new fan clutch, but it seems that when I am driving the temp stays at 1/4 but when I'm idle it climbs up. What else could be wrong with my car? Appreciate your help!

[jlevie]

A bad thermostat or a clogged radiator come readily to mind. Replace both and make sure you fully bleed the system (procedure below).

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500rpm for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

[e30conv2]

The half way mark is where most M20's run unless you have a lower degree thermostat.
Check if your getting an even flow of coolant in your tank. You may just have to bleed your cooling system. Also does the temp drop once you drive again? If so your fan clutch
is doing it's job.

[down_shift13]

yes - I have the lower degree thermostat.

yes - the temp drops once I drive again.

how do I check the thermostat? do I need a temp gun?

Also, can you clean / unclog a radiator? how do you do that?

[dnguyen1963]

A new radiator is about $170. However, if you are strapped for cash you can try the following. Remove your radiator then fill it up with bleach. Cap the radiator and let it sit overnight. Flush out the bleach and check for flow. If it is good then you are done. Otherwise, fill it up with liquid draino and let it sit overnight. Flush with water the next day. If your radiator is still clogged then throw it in the garbage. Also, check the fins. If they fall off the radiator when you are touching them then your rad is toasted.

[jlevie]

You check a thermostat by removing it from the car and slowly heating it in water while monitoring the temperature of the water. The thermostat should be fully open at it's rated temperature.

While a lower thermostat is available and can be used, The engine runs more efficiently when using the OE 80C thermostat.

Other than a flush there is no good way to clean a radiator. Replacement is the only realistic option. Which is something that should be done every 10 years or 100 just because the plastic bits get brittle and can fail. Best practice is to replace the entire cooling system every other timing belt change. And by that I mean the radiator, all hoses, thermostat, expansion tank, cap, and fan clutch.

[jeffnhiscars]

I had a car run hot on me for ages...swapped everything at least once. Turns out I had no radiator shroud :-/

[down_shift13]

thanks for all the help, I'll test the thermostat first then I'll go from there. Oh yea, I do have a radiator shroud.

[MR 325]

Just FYI, you should not need the electric fan at all to keep the car at correct temps.

(Unless using A/C)

[down_shift13]

Thanks for all your replies. My car is running good already, I replaced the thermostat earlier.
as soon as I did that, It ran normal temps with A/C. Also, I noticed that without A/C the temp increases, so I checked the Fan clutch using the magazine/paper test and as soon as I did that the mag stopped the fan. I ended up using my old clutch fan, maybe the new one I got was defective. The old clutch fan I had, kept the temps at normal.